It is well known in the art to construct flat plate heat exchangers, in which there is provided a plurality of plates arranged adjacent to each other and forming between them sealed passages for two mutually heat exchanging fluids. Flow passages are provided between the plates by virtue of transverse fluid ports formed therein, and by a rubber gasket located between each pair of facing plate surfaces. The gasket is generally of elongate, continuous form, and is arranged for seating in a preformed groove provided along the edge of each plate. The stack is assembled manually, by sliding each plate onto one or more elongate supports, so that the groove extends generally upwards, thereafter, a gasket is placed in the groove. Subsequently, an entire stack of plates and gaskets has been assembled on the supports, it is tightened together, thereby compression the gaskets between the plates so as to seal the spaces between the plates against leakage.
It is of particular importance to ensure that the gaskets are correctly positioned prior to the stack being tightened. Otherwise, the stack may not be properly sealed, leading to leakage. In the event that this happens, it is, of course, necessary to locate the improperly positioned gasket, and to partially dismantle the stack so as to align the gasket properly prior to tightening the stack once more.
Various efforts have been made to facilitate easier and more accurate placement and retention of gaskets prior to tightening.
U.S. Pat. No. 4,377,204, entitled "Plate Heat Exchanger," describes a plate heat exchanger arrangement in which the plate is formed with a plurality of holes between the gasket seating groove, and the plate edge, and wherein each gasket are provided with a plurality of tabs extending laterally outward from the main gasket portion, and wherein each tab has formed thereon a protrusion which is arranged for insertion into an adjacent hole. The protrusion is provided facing generally downwards, out of the view of a person assembling the gasket and the plate, so as to extend towards the surface of the plate in which the groove is formed, and must be pushed through the hole - away from the in order for the gasket to become properly fastened to the plate. Moreover, if the protrusions are not pushed through properly, then the gasket will not lay properly, and the extra thickness of a non-inserted protrusion may cause a slight misalignment of the gasket relative to the stack, causing an imperfect seal, and the problems caused thereby.
In an attempt to overcome this problem, U.S. Pat. No. 4,635,715, entitled "Gasket Arrangement for a Plate Heat Exchanger," teaches a gasket for placement into the gasket seating groove of a plate, and which has, on the side of the gasket closest to the plate edge, a plurality of spaced apart plate retention portions, which are arranged at a distance from each other.
This prior art gasket is illustrated in FIGS. A, B, C and D, herewith, and is denoted generally by the letter a. The main portion of gasket a, formed for seating in a groove b of a heat exchanger plate c, is indicated by the letter d. It will be appreciated that only small sections of both the gasket a and of the plate c are illustrated, and that, in the present drawings, and, indeed, through the present specification, they are intended to represent the entire gasket and plate, respectively.
FIG. A shows a section of the gasket a, and FIG. B shows proper placement thereof in groove b of heat exchanger plate c. Gasket a has a plurality of plate mounting portions e, of which a single one only, by way of illustrative example, is shown herein. Mounting portion e has one or more projections f, which are formed integrally with and perpendicular to the main gasket portion d, and thus also to the edge g of plate c. The projections f have integrally formed therewith a bridge portion h which is parallel to the main gasket portion d, and from which extend--at right angles thereto--one or more holding elements i. In the present example, a single holding element i is provided.
The holding elements i are parallel to and spaced longitudinally from the projections f and extend back towards the main gasket portion d, and therebetween, so that the projections f and holding elements i serve to effectively surround the plate edge g, such that the plate mounting portions serve to provide a retention force across the plate, and in the plane of the plate, thereby to reduce the chance of the gasket becoming detached from the plate.
A disadvantage, however, of the solution suggested in the above cited patent, is that it does not securely fasten a gasket to a plate, and, due to the relative flexibility of the gasket, does not provide sufficient purchase on the plate so as to prevent its dislodgment therefrom during assembly.
Furthermore, and referring now to FIG. C, it may happen during assembly, that the holding portion f thereof, instead of being fastened underneath the plate edge, instead remains on the top surface thereof. As now seen FIG. D, the assembling of a subsequent plate onto the improperly placed holding portion f, causes a misalignment in the assembled stack, thereby causing leakage therefrom. In practice, the misalignment is not normally discovered until use of the stack, which is a source of great inconvenience, as the system has to be properly emptied and disassembled, and, furthermore, as it is difficult to determine the location of the improperly placed holding portion, and it is required to disassemble much or all of the stack in order to determine its location.